In recent years it has been increasingly important to precisely control the temperature of a substrate such as a semiconductor wafer, a liquid crystal panel, or the like in the treatment process of the substrate. For example, in a manufacturing process of semiconductor devices, heating and cooling of a wafer are frequently performed in such a manner that, after a resist is applied to the wafer, the wafer is heated for removal of a resist solvent, and then, the wafer is cooled. For this purpose, a substrate temperature control apparatus is used for appropriately controlling the temperature of the substrate.
The substrate temperature control apparatus includes a stage having a flat upper surface for mounting the substrate thereon, and a heating device or cooling device for heating or cooling the substrate is provided inside or in the lower part of the stage. Typically, an electrically heated wire, an infrared lamp, or a working fluid is used as the heating device, and a Peltier device or a working fluid is used as the cooling device.
As a related technology, International Publication WO99/41778 discloses an apparatus for controlling the temperature of a substrate such as a semiconductor wafer, a liquid crystal panel, or the like by heating or cooling the substrate in a treatment process of the substrate. In the apparatus for controlling the temperature of a substrate, a stage on which a semiconductor wafer is placed has a vertically symmetrical structure including a thin and flat type container of a metal having a high thermal conductivity, and film type heaters attached on upper and lower surfaces of the container. The vertically symmetrical structure is adapted to prevent the flexure of the stage due to the thermal expansion thereof and improve the soaking characteristics of the substrate.
Further, Japanese Patent Application Publication JP-A-9-134776 discloses a heating apparatus applied to baking treatment of a semiconductor or a liquid crystal panel and firing of a wafer and a substrate in a film formation process. The heating apparatus includes a base plate, a plate-like heating element provided on one surface of the base plate, and a face plate provided on one surface of the plate-like heating element, and the face plate is for heating a material to be heated on a surface of the face plate by using heat conduction from the plate-like heating element. The heating apparatus is characterized in that a heat conducting element having higher heat conductivity than that of the face plate is provided between the face plate and the plate-like heating element. Specifically, the face plate is made of an aluminum material and the surface of the face plate is alumite-treated. The heat conducting element is made of copper or a copper alloy.
Although the aluminum material is softer than ceramics, the aluminum material is inexpensive and has high heat conductivity. Therefore, if the face plate of the stage can be made by employing a thin aluminum material, a substrate temperature control apparatus at low cost and with high reliability can be realized. However, in the case where the stage has the vertically symmetric structure for preventing thermal deformation of the stage, the structure becomes complex.